Direct production of polystyrene from petroleum by-product ethylbenzene



62 I Pranmter 1R5 Rubber 53 660 Nov. 12, 1957 w. w. TWADDLE ET ALPETROLEUM BY-PRODUCT ETHYLBENZENE Filed July 21, 1955 DIRECT PRODUCTIONOF POLYSTYRENE FROM Gas FURNACE Gas 2 /5 DEHYDROGENAT/ON F 43 24 n/sr.44

TOWER-- /3\ 34" 45 65 Aromatics t: 5

0 Steam Tar mu 7 uonauen L 47 sunee new 48' Benzene fffljjg'? R sToluene ":E'f'f 0 Xylene and ym E tlry/ T POLYMER/ZAT [01V .EAE RBenzene REACTOR 87 -52 OLYMER 50L SURGE DRUM IVGOH 8 Na Warren StyrenePellets INVENTORS W. Twaddle Arthur A. Harbnn Vernon W Arno/d ATTORNEYDIRECT PRODUCTION OF POLYSTYRENE FROM PETROLEUM BY-PRODUCT ETHYLBENZENEWarren W. Twaddle, Hammond, Ind., Arthur A. Harban, 'P rkForest, 1 andrnon W- Amei Hammond, hides. s ig to S a d r Oil Comp ny, Chi g 111., aco por ti n f ndian Application July 21, 1955, Serial No. 523,536 1 lams (Cl- 2.60- 3- This invention relates to an improved process for thecommercial production of polystyrenes suitable for injection mqlding,extrusion, etc. from an ethylbenzenex y lene mixture obtained in thehydroforming of naphtha without the necessity of separating ethylbenzeneor styrene frem the xylene solution. More specifically, the inventionpertains to an improved process for directly polymerizing styrene from asolution formed by selectively dehydrogenating the ethylbenzenecontained in a Xy en sol i An object of this invention is to provide animproved method and means for producing polystyrene directly from anethylbenZene-Xylene solution which has been subjeeted to defineddehydrogenation treatment and freed from tars and water. Another objectis to provide an improved polymerization and polymer recovery system.The invention will be described as applied to an integrated system anddefined in the annexed claims.

-An important object of the invention is to provide a process. formaking polystyrene from by-product petroleum ethylbenzene which does notrequire separation and purifieation of either the ethylbenzene or the.styrene monomer (other than drying) whereby the total investment andoperating costs are enormously reduced. In other words, an objective isto provide an integrated dehydrogenation and polymerization processwherein the same xylene. carrier is comon to both steps and the efiluentstream from the first step requires only removal of higher boilingcomponents (tar), lower boiling materials (gas), and water before beingcharged to the second step. An object is to provide the specificcatalysts and conditions in both the dehydrogenation and polymerizationwhich are essential for obtaining products of required properties inmaximum yields, with minimum by-product formation and at minimuminvestment and operating cost. Other objeet-s will be apparent as thdetailed description of the in en on p oce d i In practicing theinvention a Ca aromatics fraction containing about 10 to 4.0 percent,preferably about 20 to 30 percent, ethylbenzene is obtained fromhydroformed naphtha by fractionation to. eliminate higher and lowerboiling components, and to substantially eliminate hydrocarbons otherthan aromatics, the Ca aromatic fraction thus being a solution of;ethylbenzene in mixed xylenes which may have the approximate composition121:3 ortho.-, para-, and meta-xylene. To each pound of this solution atleast 2 and preferably about 2 /2 pounds of steam is added so. that thetotal charge will contain at least 1.2 and preferably about mols ofsteam per mol of solution. When lesser amounts of steam, e. g. belowabout 2 pounds per pound of aromatics, are employed, the activity of thedehydrogenation catalyst decreases rapidly with, time, lowering theconversion to styrene. Ratios; of steam to aromatic substantiallygreater than 2 pounds per pound may be employed but they give little orno improvement in styrene yield. The steam may be added either to the.cold liquid aromatic hydrocarbon mixture or to an aromatic charge whichhas been heated to a temperature above its varporization point.Preferably, the steam is added when the hydrocarbon vapors are at atemperature of about 150 C. and the mixture of vapor and steam is thenpreheated in an exchanger to a temperature in the range of about 430 to530 C. and then passed to a direct-fired furnace wherein the mixture isheated to about 670 to 730 C., e. g. about 700 C., with a residence timein the furnace of a fraction of a second, preferably not more than about/2 second since times substantially greater than this lead to excessivecracking. Temperatures above 730 C. lead to excessive cracking and lowerultimate yields of styrene while temperatures below 670 C. lead todecreased styrene yield because of lowered catalyst activity and failureof the catalyst to be auto-regenerative.

The catalyst employed for the dehydrogenation is pref-- erably asteam-regenerative, alkali-promoted iron catalyst of the type commonlyknown in the art as Shell 105 or Shell 205. Such a catalyst may consistessentially of percent F6203, 2 percent C1'2O3 ,12 percent KOH and 1percent NaOH or of percent FezOa, 4 percent Cr203 and 6 percent K2003;the catalyst compositions and the method of making same are disclosed inU. S. 2,408,140, 2,414,585 and 2,461,147. While these known commercialdehydrogenation catalyst are preferred, the invention is not limitedthereto and other known steamregenerative dehydrogenation catalysts suchas Jersey 1707 may be employed (Ind. Eng. Chem. 42, No. 2, pp. 295 etseq.; 1950).

The dehydrogenation is preferably effected at a pressure in the range ofabout 1 to 10 p. s. i. g. and with a space velocity of about 0.5 to 4volumes of liquid aro matic chargingstock per hour per volume ofcatalyst. Dehydrogenation may be eifected in either an isothermal or anadiabatic catalyst bed, an isothermal bed at about 700 C. beingpreferred for optimum yields of styrene. The residence time ofhydrocarbon in the dehydrogenation reactor should be :of the order ofabout .1 to .6 second.

The dehydrogenation reactor effiuent is immediately cooled, for example,to about 300 to 320 C., then further cooled, for example, to about 50 C.for condensation of liquids from gases, the gases being furtherrefrigerated for recovery of styrene and aromatics contained therein.After separating Water from the condensate the latter is distilled-toobtain a solution of styrene in xylenes which contains someethylbenzene, toluene and benzene and which, after drying but withoutany further purification or separation, may be introduced directly intoa polymerization reactor wherein the styrene monomer is converted tohigh molecular weight polymer by contact with a catalyst consistingessentially of finely divided metallic sodium. The use of this type ofcatalyst in the polymerization step is important since neither thermalpolymerization, free radical polymerization or polymerization with acidtype (Friedel-Crafts) catalysts were eifective for obtaining polystyreneof desirable properties in feasible yields in the Xylene solution. Withfinely divided sodium catalyst, i. e. sodium particle about 1 to 100,preferably 2 to 50, microns particle size, dispersed, for example, in.about an equal weight of xylene or other diluent and employed in amountsof about .1

. to .6 percent, preferably about 0.2 to .4 percent by weight based onstyrene, conversions upwardsof 90 percent are obtained in 5 to 30minutes or more after an induction period of 5 to 20 minutes) givingpolystyrenes of various molecular Weights depending primarily. upon thetemperature maintained in the polymerization step. At about C. polymershaving an intrinsic viscosity (asmeasured in benzene at 30 C.) of about0.1 are obtained while at 60 C. the intrinsic viscosity of the polymeris of the order of 1.0. Thus by effecting polymeriza tion at acontrolled temperature in the range of about 40 to 100 C. (40 to 75 C.,preferably 40 to 65 C. for molding grade) with finely divided sodium,any desired molecular weight of polystyrene may be obtained from whichthe minute amount of catalyst can be readily separated by filtrationfrom the xylene solution.

In order to obtain a styrene polymer of more uniform intrinsic viscosityor molecular weight, it is desirable after about 60, percent of themonomer has been polymerized, e. g. at 50 C.,.to either gradually lowerthe polymerization temperature, e. g. to about 40 C., and/ or to add apromoter or polymerization accelerator such as a low boiling aliphaticor cyclic ether, e. g. dimethylether. The heat of polymerization isremoved by vaporizing a part of the monomer solution at controlledsubatmospheric pressure and a feature of the process is that thevaporizationof diluent does not alter the concentration of monorrier inthe solution since the styrene monomer has substantially the sameboiling point as the xylene diluent so that, regardless of fluctuationsin the rate of vaporiza tion, the temperature can be maintainedsubstantially constant and, at the same time, concentration of monomerin vapors is always substantially the same as that in the liquid phase.

The polymerization is preferably effected batch-wise and while the majoramount of polymerization may be effected in about /2 hour or less, it isusually desirable to continue the reaction for a period of 1 to 3 hourswith the latter part of the reaction at decreased tempera ture which isattained by increasing the vacuum applied to the polymerization reactor.This technique enables the polymerization of substantially all of themonomer without forming large amounts of low molecular weight polymer atthe end of the reaction period.

When reaction has been completed the viscous polymer solution is eitherfiltered to remove sodium and sodium hydroxide or treated withNa2SO4.6HzO for insuring conversion of residual sodium to sodiumhydroxide and then treated with NaHSOa to effect conversion of thesodium hydroxide to sodium sulfate and water, the water being removed bycontacting with a suitable diluent such as bauxite. When it is desiredto obtain a polystyrene of high impact strength it may be desirable toadd about 2 to 20 percent of synthetic or natural rubber to thecatalyst-free solution at this point. This catalyst-free solution isthen heated to a temperature of about 200 to 300 C., preferably about250 to 275 C. and most of the solvent is removed therefrom in a flashdrum at about .1 to 1 atmosphere pressure. The remaining viscoussolution which may be about 3 parts polymer and 1 part solvent is thenextruded in thin streams into a vacuum chamber maintained at about 1 to50 mililmeters, preferably 2 to 20 millimeters, absolute pressure forcompleting the removal of solvent and the substantially solvent-freepolymer is then extruded through a cooling zone to a pelleting machine.

The solvent removed in the flash and vacuum drying, together withsolvent removed in maintaining the vacuum on the reactor, is treatedwith clay maleic anhydride or other known means to remove any unreactedstyrene monomer and the solvent is then fractionated to recover benzeneand toluene formed in the system, unreacted xylenes which wereintroduced with the original charge and any bottoms material.

The invention will be more clearly understood from the followingdetailed description of a specific example thereof read in conjunctionwith the acompanying drawing which is a schematic flowsheet of thesystem for producing styrene from a petroleum by-product ethylbenzenestream.

While any source of ethylbenzene-containing Ca aromatics may beemployed,such aromatics are preferably obtained by extracting aromatics from anaphtha hydroforming process such, for example, as hydroforming,platforming, ultraforming, andthe like, preferably employing apolyethylene glycol solvent as exemplified by the commercial Udexprocess. The extract, after removal of solvent, is then fractionated bydistillation to remove from the C8 aromatics substantially allhydrocarbons which are higher boiling and lower boiling. A Ca aromaticsfraction is thus obtained which is substantially free from otherhydrocarbons and which may consist of about 20 to 30 percentethylbenzene mixed with xylenes having the approximate composition 1:1:3ortho-, para-, meta-xylene. Alternatively a hydroformed naphtha mayfirst be distilled to obtain a Ca fraction and aromatics may then beseparated from the Ca fraction by adsorption, extractive distillation orother separation means known to the art.

The Ca aromatics stream obtained as hereinabove described, which in thisexample contains 28 percent ethylbenzene, may be vaporized and heated toabout 150 C., and introduced through line 10 and about 2 /2 pounds ofsteam is introduced through line 11 for each pound of aromatics so thatthe mol ratio of steam to aromatics will be at least 12:1 and preferably15:1 or more. The mixture of steam and aromatics is then preheated inexchanger 12 to a temperature of about 500 C. after which the preheatedmixture is charged by line 13 to furnace 14 which is preferably adirect-fired vertical-tube Petrochem furnace wherein it is furtherheated to about 700 C. during its contact time in the furnace tube ofapproximately /2 second. The hot mixture then passes through line 15 todehydrogenation reactor 16 which contains Shell 205 steam-regenerative,alkali-promoted iron oxide catalyst. The reactor is preferably oftubular design with indirect heating so that the endothermicdehydrogenation reaction may be carried out essentially isothermally,the catalyst being mounted in tubes and a heating fluid such, forexample, as flue gas from furnace 14 being passed around the tubes formaintaining the temperature at the desired level of about 700 C. If anadiabatic reactor is employed, the temperature drop across the catalystbed may be as much as about 50 C. and in such case it would be preferredto employ a reactor inlet temperature of about 730 C. In this examplethe dehydrogenation reactor is operated substantially isothermally atabout 700 C. with an inlet pressure of about 6 p. s. i. g., a spacevelocity of about 2 volumes of aromatics per hour per volume of catalystspace and a residence time in the reactor of about second.

The reactor efliuent is immediately cooled in exchanger 12 to atemperature of about 310 to 320 C. and is then passed by line 17 throughcooler 18 which cools the mixture to a temperature of about 50 C. atwhich temperature the cooled mixture is introduced into separator 19.Gas from the separator, chiefly steam, hydrogen, carbon dioxide,methane, Cz+ hydrocarbons and some aromatics, is removed from theseparator through line 20 to condenser 21 which cools these gases to atemperature of about 30 C. for effecting further condensation, thecooled mixture being introduced into separator 22. Gases are removedfrom separator 22 through line 23 to cooler 24 wherein the gases arefurther cooled to about 0 to -10 C. for effecting still furthercondensation, the mixture from cooler 24 being introduced to separator25 and gases vented from the system through line 26. Condensate fromseparator 25 is returned by line 27 to separator 22. Condensate fromseparator 22 is returned by line 28 to line 29 which withdraws liquidfrom separator 19, the combined liquids being introduced into separator30 for separating an aqueous phase which is withdrawn through line 31and a liquid hydrocarbon phase which is introduced by lines 32, 36 and33 at the base of distillation tower 34 below a trap-out plate 35 whichis in the lower part of the tower. Liquid which collects in the trap-outpan-35 passes by line 36 through reboiler 37 and thence by line 33 backto the base of the tower to supply the heat required for vaporizing thediluted styrene. Materials, higher boiling than C; aromatics (i. e.

. tar) are withdrawn from the base of tower 34 through line 38. Allother materials are taken overhead through line 39 and cooler 40 toreceiver 41 from which gas may be vented by line 42. Liquid may beremoved from receiver 41 by pump 43, a part of it being returned by line44 to serve as reflux in the distillation tower and the remainderthrough line 45 to monomer solution surge drum 46. In this particularexample about 17 pounds of gases are vented through line 26 and about 2pounds of tarry bottoms are removed through line 38 per hundred poundsof C aromatics charged. The intermediate product in surge drum .46consists essentially of -25 percent or about percent styrene, about 5percent unconverted ethylbenzene, about 9 percent toluene and about 3percent benzene, the yield of styrene based on initial ethylbenzene be npp ox ma el 5 e ght p s n From the foregoing description it will be seenthat the dehydrogenation step otters many unique advantages. Under thedefined conditions the dehydrogenation catalyst is autoregenerative sothat the dehydrogenation systern may be operated continuously Withoutthe necessity of interrupting charging stock flow through the reactorfor effecting regeneration. The styrene yields are of a higher order ofmagnitude than have heretofore been attainable in ethylbenzenedehydrogenation systems Only about 5 percent of the initial hydrocarboncharge was converted to gas and both the xylene diluent and the steamserve as heat carriers and diluents for improving the effectiveness ofdehydrogenation. If pure ethylbenzene were employed without the addedbenefit of xylene diluent, the maximum single pass conversion ofethylbenzene to styrene would only be about 60 percent while in thedefined process employing both steam and xylene diluent, styrene yieldsin a single pass of about 75 percent or higher can be obtained.

Heretofore commercial polystyrene processes have all required separationand purification of styrene monomer which required large capitalinvestment and operating expense and which presented innumerableprocedural and control difficulties. In the present invention no suchseparation or purification of styrene monomer is necessary. The crudelyseparated xylene solution of styrene monomer is simply passed by line 47through a dryer which may, for example, be alternate towers 48 and 48'containing a desiccant such as bauxite for decreasing the water contentof the xylene solution to below 50 parts per million, preferably toabout 20 parts per million. The dried solution is then introduced byline 50 into polymerization reactor 51 which is provided with a stirrer52 driven by motor 53. The reactor is preferably operated batch-Wise sothat when a reactor charge is thus introduced a valve in line 5th isclosed and the reactor is evacuated by withdrawing gases and vaporsthrough line 54 and cooler 55 to separator 56, the condensed vaporsbeing returned to the reactor by line 57 and uncondensed gases beingwithdrawn through line 58 by pump 59 which discharges through line 60.Obviously, the desired vacuum may be obtained by water or steam eductoror any other known means instead of by pump 59. The extent to which thereactor is evacuated is determined by the type of polymer to beproduced. Thus, for producing a molding grade polymer having anintrinsic viscosity (n) of about 1.0 and an impact strength asdetermined by the Izod method of about .2-.3, the desired polymerizationtemperature may be about 50 C. and evacuation by line 59 is continueduntil the liquid in the reactor is boiling free at the desiredtemperature. When the degree of vacuum and desired polymerizationtemperature have thus been attained, finely divided sodium catalystdispersed in xylene is introduced through line 61 to obtain about .3weight percent sodium based on the total styrene monomer in the reactorcharge. As above stated, the sodium should have a particle size lessthan 100 microns, the average particle size in this example being about20 microns, and the introduced sodium dispersion containing about 50percent by weight sodium in xylene.

With the stirrer maintaining an intimate mixture of the introducedcatalyst in the solution of styrene and xylene and the temperature beingmaintained substantially constant, at 50 C. in this example, by slightboiling of the solution, about 5 to 20 minutes elapse before thepolymerization reaction commences. After this induction period thepolymerization rate is extremely rapid and the vapor removal andcondensing system (elements 54, 55, 56 and 57) must be adequate torecover, condense, and return all liberated vapors Without substantialchange in pressure in the reactor system which during this time ismaintained substantially constant by evacuating means 59. Whenapproximately 60 percent of the styrene monomer has been converted intopolymer (which may be determined by testing samples periodicallywithdrawn from the reactor for viscosity or for styrene content) thepressure in the reactor is decreased by increasing the applied vacuum sothat the polymerization temperature is gradually decreased to about 40'C. and held at this lower temperature for approximately 1 hour. Insteadof, or in addition to, decreasing the reaction temperature, a reactionpromoter such as methylethyl or dimethylether may be introduced throughline 62 in amounts sufficient to prevent the polymers formed during thelatter part of the polymerization period from being substantially lessviscous or of substantial lower molecular weight than polymers formed inthe initial stage of the polymerization.

When the polymerization reaction is substantially complete, the viscouspolymer solution is pumped from the base of the reactor by pump 63 tofilter 64 which is precoated with celite or other inert filter aidmaterial of high surface area effective for removing unreacted sodiumand sodium hydroxide from the solution, the filter aid with removedcatalyst being withdrawn through line 65. While filtration through afilter aid material is a preferred method of eliminating catalyst,alternative methods may be employed; the solution may be passed througha bed of NazSOsel-IzO for insuring conversion of sodium to sodiumhydroxide and then through NaHSOq. to convert sodium hydroxide to sodiumsulfate with liberation of water and finally, through a desiccant bedsuch as bauxite for removing the water.

The catalyst-free solution is withdrawn from the filter through line 66to polymer solution surge drum 67 and if it is desired to produce apolystyrene of high impact properties, about 10 percent of GRS rubbermay be added to the polymer solution in line 66 through line 66a so thatthe rubber is intimately mixed with the polymer solution when it reachesthe surge drum. Polymer solution is introduced from the surge drum bypump 68 through line 69 to heater 70 wherein the solution is heated to atemperature of about 260 C. and the heated solution is then introducedinto flash tower 71 from which solvent is removed through line 72 bypump 73 at a rate to maintain a flash drum pressure of about 6 p. s. i.a. (although atmospheric distillation may be employed at this stage).Most of the solvent is thus removed from the polymer solution and theremaining solution, which now is about 75 percent polystyrene in xyleneis passed through line '74 through distributor nozzles or orifices 75 invacuum drum 76, sufiicient heat being added at distributors 75 or in thevacuum drum to maintain the temperature in the vacuum drum at about 100.to 250 0, preferably about 200 C. Solvent vapors are removed from thevacuum drum by line 77 and pump 73 for maintaining the absolute pressuretherein less than 50 millimeters of mercury, preferably about 10millimeters of mercury. The thin streams of polymer which emerge fromdistributor nozzles or orifices are thus substantially denuded ofsolvent before they reach the base of the vacuum drum.

The solvent-free polymer is picked up at the base of the vacuum drum byan extruder 79 driven by motor 8%, the extruder providing the necessaryseal for maintaining the high vacuum and discharging a hot rod or ribbonof polystyrene 81 which contains less than 1 percent 'xylene and whichis preferably cooled in an inert, e. g., nitrogen, atmosphere or byspraying a cooling fluid such as water or a cold inert gas thereon fromdistributors 82. The cooled polystyrene ribbon or rod is then pelletedby conventional means in pelleting equipment 83 for obtaining thestyrene pellets of desired size and the pellets are discharged by line84.

Solvent discharged by pumps 73 and 78 may be introduced by line 85through suitable condensers (not shown) to solvent-treating system 86for removing any unreacted styrene monomer by contact with clay,reaction with maleic anhydride or by any other conventional means. Thestyrene-free solvent then passes by line 87 to a fractionation systemdiagrammatically represented by tower S8 for separating a lightbenzene-toluene fraction through line 39, a Xylene-ethylbenzene fractionthrough line 90 and a bottoms fraction through line 91.

From the foregoing description it will be seen that most of the xylenesoriginally introduced with the ethylbenzene through line 10 serve animportant function in increasing styrene production in thedehydrogenation reactor, serve the function of a styrene carrier forintroducing the monomer to the polymerization step, serve as arefrigerant of styrene boiling range in the polymerization reactor andserve as a polymer diluent which enables catalyst separation from thepolymer, the bulk of the xylenes finally being obtained as one of theproduct streams discharged through line 90. Only a small amount of thetotal Cs aromatics is converted to gas, benzene and toluene in thedehydrogenation step, most of the xylene diluent being ultimatelyrecovered from the original charge in the final solvent distillationstep. Thus the polystyrene process of this invention for the first timemakes it practically feasible on a commercial scale to prepare highquality molding grade polystyrene from petroleum by-product ethylbenzenein a manner which is enormously simpler and less expensive than anycommercial styrene process heretofore known to the art.

In a pilot plant demonstration of the process of this invention acharging stock was employed containing about 28 percent ethylbenzene ina mixture of ortho-, meta-, and paraxylenes produced by Udex extractionof hydroformed naphtha, the infrared analysis of the charging stockbeing set forth in the following table. The pilot plant run wascontinued for 190 hours using 2 liters of Shell 205 catalyst ashereinabove described. It was conducted isothermally at about 1300" F.with a liquid hourly space velocity of about 0.84 and with about a 25:1steam-to-hydrocarbon weight ratio under a reactor pressure of about 3 p.s. i. g. Infrared analyses of the products produced at various runintervals are shown in the following table:

It will be noted that throughout the run the yield of styrene was about75 weight percent based on ethylbenzene charged; laboratorydehydrogenation runs have shown that even higher conversions ofethylbenzene to styrene may be efiected under the defined conditions sothat in commercial operations ethylbenzene to styrene conversions of atleast 70 weight percent and usually as about 75 weight percent or highershould be attainable with gas losses based on total hydrocarbon chargeamounting to substantially less thanabout 5 percent by weight. Theattainment of such conversions on a once-through basis demonstrates theremarkable effectiveness of the defined dehydrogenation technique.

A composite of the product obtained in the pilot plant dehydrogenationrun was fractionated at reduced pressure and at .5 reflux ratio toremove tars; in the experimental work about 90 percent of the charge wastaken overhead although in commercial operation about 98 percent or moreof the liquid dehydrogenation product would be taken overhead. Thecondensed overhead stream contained 23.2 Weight percent styrene byultraviolet analysis. This material was' dried by percolation overalumina and then polymerized by dispersed sodium in xylene, the particlesize of the dispersed sodium being in the range of 5 to 50 microns, i.e. about 20 microns, and the sodium being added in an amount sumcient togive 0.13 weight percent sodium based on styrene monomer. Vacuumrefluxing was applied to maintain the polymerization temperature at 50C. The polymerization was continued for about 3 hours. Catalyst wasremoved from the polymer solution by filtration through a celite-coatedfilter using 50 p. s. i. g. pressure. The yield was about 93 weightpercent based on monomer charged and its intrinsic viscosity (measuredin benzene at 30 C.) was 0.97. A molded sample of the polymer had goodclarity and color.

The specific example was directed to the manufacture of molding gradepolystyrene at a polymerization temperature of about 50 C. and anabsolute pressure of about 30 millimeters of mercury. By incorporatingrequired amounts of natural or synthetic rubber into the polymersolution before removing solvent therefrom, a difierent grade of polymermay be obtained which is characterized by an intrinsic viscosity (n) ofabout .7 to 1.3 and with an impact value as determined by the Izodmethod of 0.5 to 8.0. The natural or synthetic rubber may be introducedinto polymerization reactor 51 prior to or during styrene polymerizationinstead of to line 66. When polymerization is effected at a temperatureof the order of C., a floor tile grade of polystyrene may be obtainedwhich is characterized by an intrinsic viscosity in the range of about0.15 to 0.5. By proper control of reaction temperature and/ or by theuse of known accelerators and catalyst modifiers, various other typesand grades of polystyrene may be produced. Furthermore, fillers,pigments and the like may be incorporated in the polystyrene solutionprior to removal of solvent therefrom for making polystyrene pellets forspecific molding purposes. The sodium catalyst may be removed from thepolymer solution by water washing instead of by the techniquesheretofore described. The polystyrenes produced with dispersed sodiumcatalyst are, of course, free from residual peroxides which tend tocause greater instability when exposed to light. ther advantages andalternative steps and conditions will be apparent from the abovedescription to those skilled in the art.

We claim:

l. The method of making polystyrene from ethylbenzene contained in a C8aromatic stream obtained from hydroformed naphtha which method comprisesdehydrogenating saidethylbenzene in the presence of Ce aromatic diluentsto obtain an aromatic solution of styrene monomer which is substantiallyfree from tar and water and which contains about 15 to 25 percentstyrene, contacting said aromatic solution of styrene monomer with afinely divided dispersed sodium catalyst at a controlled temperature inthe range of about 40 to 75 C., controlling the temperature in thepolymerization step by boiling solution the major portion of the solventfrom the remaining polymer solution, removing substantially all of theremaining solvent from the solution by exposing thin streams ofconcentrated polymer solution to a temperature in the range of about 100to 250 C. under a pressure less than 50 millimeters of mercury andcooling the substantially solvent-free polymer.

2. The method of claim 1 which includes the step of adding about 2 to 20percent of a rubber selected from the class consisting of natural rubberand synthetic rubber into the styrene monomer solution beforepolymerization thereof is completed.

3. The method of claim 1 which includes the step of adding about 2 to 20percent of a rubber selected from the class consisting of natural rubberand synthetic rubber to the solution of polystyrene in aromatic diluentafter catalyst has been separated from said solution.

4. The method of claim 1 which includes the step of decreasingpolymerization temperature when about 60 percent of the styrene monomerhas been polymerized.

5. The method of claim 1 wherein sodium catalyst is removed from polymersolution by filtration.

6. The method of claim 1 wherein sodium catalyst is removed from thepolymer solution by washing with water.

7. The method of claim 1 wherein sodium catalyst is removed from thepolymer solution by passing the solution through a bed of Na2SO4.6HzOfor converting sodium to sodium hydroxide, then through NaHSO4 toconvert sodium hydroxide to sodium sulfate with liberation of water andfinally through a desiccant for removing the liberated water.

8. The method of claim 1 which includes the step of introducing areaction promoter during the polymerization step after about 60 percentof the styrene monomer has been polymerized.

9. The method of claim 1 which includes the step of cooling thesubstantially solvent-free polymer in the presence of an inert coolingfluid.

10. The method of claim 1 which includes the steps of recovering solventremoved from styrene polymer and fractionating said solvent to recoverxylenes introduced with initial ethylbenzene.

11. The method of making polystyrenes which comprises adding to Caaromatics containing to 40 percent ethylbenzene and separated fromproducts of naphtha hydroforming about 2 /2 parts by weight of steam perpart of Ca aromatics, preheating said mixture to a temperature of theorder of 500 C., then increasing the temperature of the preheatedmixture to about 700 C. in a small fraction of a second and contactingthe hot mixture in a reaction zone at a temperature of approximately 700C. and under a pressure in the range of about 1 to 10 p. s. i. g. with asteam-regenerative, alkalipromoted iron oxide dehydrogenation catalystat a space velocity in the range of about .4 to 4 volumes of liquidcharge solution per volume of catalyst space per hour with a hydrocarbonresidence time in the reaction zone of about .2 to .6 second, separatinggases, water and tar from the dehydrogenated product stream, then dryingsaid product stream and introducing it into a polymerization zone,reducing the pressure in the polymerization zone to a level at which thedried product stream boils at a predetermined temperature in the rangeof 40 to 75 C., introducing about .1 to .6 weight percent of finelydivided sodium dispersed in a solvent into the dried dehydrogenationproduct stream in the polymerization zone and intimately admixing theintroduced catalyst with said dried dehydrogenation product stream,removing heat of polymerization by boiling liquids in the polymerizationzone, removing the resulting vapors as fast as they are liberated,condensing vapors and returning condensate while maintaining thepolymerization zone at the pressure required for maintaining thepredetermined temperature, separating catalyst from polymer solutionwhen polymerization is completed, and removing solvent from saidsolution to obtain a polymer containing less than 1 percent solvent.

12. The method of claim 11 which includes the step of removing most ofthe solvent from the catalyst-free polymer solution by distillation toobtain a more viscous polymer solution and discharging the viscoussolution in thin streams through orifices into a Vacuum chamber at atemperature in the range of about 100 to 260 C. under a pressure lessthan 50 millimeters of mercury.

13. The method of making polystyrene which comprises preparing asolution of about 15 to 25 percent styrene in aromatic hydrocarbonscontaining; not more than 8 carbon atoms per molecule, which solution issub stantially free from higher boiling components and which containsless than 50 parts per million of water, polymerizing the styrene insaid solution at a temperature in the range of about 40 to C. which iscontrolled by vaporizing solvent and monomer in a polymerization zone atregulated subatmospheric pressure, condensing the vaporized solvent andmonomer and returning the condensed vapors to said zone, the styrenemonomer having about the same boiling point as the aromatic solvent sothat the styrene concentration is substantially the same in the liquidand vapor phases, effecting said polymerization with dispersed metallicsodium in an amount in the range of about .1 to .6 weight percent basedon styrene, and in the presence of an ether promoter, separating thesodium from the resulting polymer solution, removing most of the solventfrom the solution to give a concentrated polymer solution and passingsaid concentrated solution in at least one thin stream through a vacuumzone to an extruder outlet, said vacuum zone being under a pressure notsubstantially higher than 50 millimeters of mercury and at a temperaturein the range of about to 250 C. for removing the remainder of thesolvent.

14. The method of claim 13 which includes the step of adding about 2 to20 percent of a rubber selected from the class consisting of naturalrubber and synthetic rubber into the styrene monomer solution beforepolymerization thereof is completed.

15. The method of claim 13 which includes the step of adding about 2 to20 percent of a rubber selected from the class consisting of naturalrubber and synthetic rubber to the polystyrene solution after separationof sodium therefrom.

References Cited in the file of this patent UNITED STATES PATENTS2,181,771 Scott Nov. 28, 1939 2,245,619 Stearn June 17, 1941 2,425,501Wiley Aug. 12, 1947 2,540,996 Ryden Feb. 6, 1951 2,574,439 Seymour Nov.6, 1951 OTHER REFERENCES Boundy-Boyer: Styrene, its Polymers, etc.,pages 35-36, Reinhold (1952).

1. THE METHOD OF MAKING POLYSTYRENE FROM ETHYLBENZENE CONTAINED IN A C8AROMATIC STREAM OBTAINED FROM HYDROFORMED NAPHTHA WHICH METHOD COMPRISESDEHYDROGENATING SAID ETHYLBENZENE IN THE PRESENCE OF C8 AROMATICDILUENTS TO OBTAIN AN ORMATIC SOLUTION OF STYRENE MONOMER WHICH ISSUBSTANTIALLY FREE FROM TAR AND WATER AND WHICH CONTAINES ABOUT 15 TO 25PERCENT STYRENE, CONTACTING SAID AROMATIC SOLUTION OF STYRENE MONOMERWITH A FINELY DIVIDED DISPERSED SODIUM CATALYST AT A CONTROLLEDTEMPERATURE IN THE RANGE OF ABOUT 40 TO 75*C., CONTROLLING THETEMPERATURE IN THE POLYMERIZATION STEP BY BOILING SOLUTION THEREIN UNDERREFLUX CONDITIONS AT CONTROLLED SUBATMOSPHERIC PRESSURE, SEPARATINGCATALYST FROM THE RESULTING, POLYMER SOLUTION AFTER THE POLYNERIZATIONSTEP, DISTILLING THE MAJOR PORTION OF THE SOLVENT FROM THE REMAININGPOLYMER SOLUTION, REMOVING SUBSTANTIALLY ALL OF THE REMAINING SOLVENTFROM THE SOLUTION BY EXPOSING THIN STREAMS OF CONCENTRATED POLYMERSOLUTION TO A TEMPERATURE IN THE RANGE OF ABOUT 100 TO 250*C. UNDER APRESSURE LESS THAN 50 MILLIMETERS OF MERCURY AND COOLING THESUBSTANTIALLY SOLVENT-FREE POLYMER.